In recent years, hybrid vehicles are receiving widespread attention as environmentally friendly vehicles. As motive power source thereof, the hybrid vehicles use, in addition to a conventional engine, an electric power storage apparatus (battery), an inverter, and an electric motor (motor) driven by the inverter.
Among such hybrid vehicles, a hybrid vehicle having an externally charging function for charging the battery using an external power supply is known. The hybrid vehicle having the externally charging function can provide an advantage of reducing the frequency of visiting a filling station for charging fuel, for example if the battery can be charged from a household commercial power supply.
Japanese Patent Laying-Open No. 8-154307 discloses a hybrid vehicle provided with such an externally charging function. The hybrid vehicle includes: a battery that is capable of being charged from an external charger; an electric motor powered by the battery to drive wheels; control means for controlling the operation of the electric motor; an internal combustion engine that is directly or indirectly used for driving the wheels; and traveling time related amount calculation means for calculating an amount related to a traveling time from charging of the battery by the external charger. The control means limits the output of the electric motor when the traveling time related amount calculated by the traveling time related amount calculation means reaches a prescribed amount.
In the hybrid vehicle, when the vehicle travels for a long time without being charged from an external source, the output of the electric motor is limited, and necessarily, when traveling is continued using fuel by the internal combustion engine, the output of the electric motor is limited. Therefore, the driver is prompted to perform external charging. Accordingly, with the hybrid vehicle, dependence on the internal combustion engine can be reduced.
The hybrid vehicle disclosed in Japanese Patent Laying-Open No. 8-154307 reduces the dependence on the internal combustion engine. In other words, the externally charged power is used by priority. However, Japanese Patent Laying-Open No. 8-154307 does not particularly consider about the electricity costs of charging from an external source. It is a critical problem for the hybrid vehicle provided with the externally charging function to reduce the electricity costs.
The electricity price is generally inexpensive in a late-night electricity time slot where power consumption is small. If charging is performed in a time slot where the electricity price is inexpensive, the electricity costs can be reduced. Conversely, when charging must be performed in a time slot where the electricity price is expensive, it is preferable to minimize the charging amount in light of cost reduction.